Magnetic seal for a rotary shaft and magnet therefor

ABSTRACT

A magnetic seal for a rotary shaft includes a cylindrical magnetic member surrounding the shaft. The magnetic member includes an outer circumferential seal cooperating with a housing through which the shaft projects. A cylindrical magnetically attractive member also surrounds the shaft and includes an inner circumferential seal cooperating with the shaft. The magnetically attractive member rotates with the shaft and the magnet is stationary with the housing. A sealing member is interposed between the magnet and the magnetically attractive member. Magnetic attraction between the magnet and the magnetically attractive member draws the two members together to form a seal with the interposed sealing member. The magnet is molded of anisotropic ferrite permanent magnet material which is oriented in a radial direction during molding and is also radially magnetized.

United States Patent [191 Baermann 51 Jan. 2, 1973 1541 MAGNETIC SEALFOR A ROTARY SHAFT AND MAGNET THEREFOR [76] Inventor: Max Baermann, 506Bensburg,

Cologne, Germany [22] Filed: June 17, 1970 [21] Appl. No.: 47,024

[52] US. Cl. v.277/80, 148/103, 264/24, 264/D1G. 58 [51] Int. Cl. ..Fl6j15/54 [58] Field of Search ...335/302, 296; 277/80; 251/65; 29/607, 608;148/103; 264/24, DIG. 58

Primary Examiner-Robert G. Nilson Attorney-Meyer, Tilberry and Body [57]ABSTRACT A magnetic seal for a rotary shaft includes a cylindricalmagnetic member surrounding the shaft. The magnetic member includes anouter circumferential seal cooperating with a housing through which theshaft projects. A cylindrical magnetically attractive member alsosurrounds the shaft and includes an inner circumferential sealcooperating with the shaft. The magnetically attractive member rotateswith the shaft and the magnet is stationary with the housing. A sealingmember is interposed between the magnet and the magnetically attractivemember. Magnetic attraction between the magnet and the magneticallyattractive member draws the two members together to form a seal with theinterposed sealing member The magnet is molded of anisotropic ferritepermanent magnet material which is oriented in a radial direction duringmolding and is also radially magnetized.

16 Claims, 8 Drawing Figures PATENTEDJM 2191s SHEET 1 OF 3 LEE;

INVENTOR.

MAX BAERMA IVN 772%, 741W 4 50% ATTORNEXS PATENTEDJAH 2 I975 3.708.177

SHEET 2 BF 3 INVENTOR. MAX BAERMAN/v ATTORNEYS PATENTEIJJAN 2:9153108,17?

SHEEI 3 OF 3 INVENTOR. MAX BAERMA/V/V ATTORNEYS MAGNETIC SEAL FOR AROTARY SHAFT AND MAGNET THEREFOR BACKGROUND OF THE INVENTION Thisapplication pertains to the art of magnetic seals for rotary shafts andmagnets for use therein. The invention is particularly applicable forsealing rotary shafts where pressure differentials exist although itwill be appreciated that the invention has broader applications and maybe used in other environments.

Magnetic seals for rotary shafts commonly include a first elementdefined by a cylindrical sleeve magnetic member surrounding the shaftand a second element defined by a cylindrical sleeve magneticallyattractive member surrounding the shaft. One of the members is rotatablewith the shaft and the other members is fixed against rotation relativeto the shaft. A sealing means is interposed between the shaft and theone member which rotates with the shaft, and another sealing means isinterposed between the magnet and the magnetically attractive member. Atleast one of the members is shiftable axially of the shaft underinfluence of magnetically attractive force between the magnet and themagnetically attractive member.

In previous arrangements of the type described, the cylindrical sleevemagnet has been magnetized in a direction across its diameter so as tohave a north magnetic pole at one location on the periphery thereof anda south magnetic pole diametrically opposite the north magnetic pole onthe periphery thereof. With such magnetization, the lines of magneticflux extend circumferentially in the walls of the magnet. With such anarrangement, during relative rotation between the magnet and themagnetically attractive member, pole changing occurs continuously in themagnetically attractive member. That is, one point on the magneticallyattractive member continuously changes during rotation thereof frombeing influenced by the north magnetic pole to the south magnetic pole.This movement of the magnetically attractive member through the magneticfield produces eddy currents in the magnetically attractive member.These eddy currents can cause the magnetically attractive member tobecome hot, and damage to the sealing means may occur. In addition, theeddy currents produce their own magnetic field which operate inopposition to the magnetic field of the magnet and tend to demagnetizeit. Therefore, the magnetically attractive force between the magnet andthe magnetically attractive member is reduced by the opposing magneticfields produced by the eddy currents. At a sufficiently high relativerate of rotation, the magnetic attraction between the magnet and themagnetically attractive member will be reduced to substantially zero dueto the opposite magnetic field produced by eddy currents.

lt would be desirable to have a magnetic seal for rotary shafts which isnot subject to the problems described.

SUMMARY OF THE INVENTION In accordance with the present invention, ashaft seal of the type described is provided with an improvedcylindrical magnet molded of anisotropic ferrite permanent magnetmaterial including magnetic particles and a plastic binder. Morespecifically, a powdered magnetic material is mixed with a thermoplasticmaterial and the mixture is heated so that the plastic is in a fluidstate. The mixture is then injected into a mold which is shaped to forma substantially cylindrical sleeve magnet having radially spaced innerand outer circumferential surfaces and opposed end surfaces. Thematerial in the mold, while it is in a fluid state, is subjected to amagnetic field acting radially around the entire circumference. Thisaligns the magnetic particles radially in the preferred direction oftheir easy magnetization so that the cylindrical magnet will haveimproved magnetic strength in that direction. Upon cooling of theplastic material and removal of the mixture from the mold, thecylindrical magnet member is also radially magnetized. That is, thecylindrical member is magnetized so that its entire outercircumferential surface defines one magnetic pole and its entire innercircumferential surface defines another magnetic pole. With such amagnet, the magnetic field acts substantially radially along curvedlines extending from the outer circumferential surface to the innercircumferential surface outwardly of an end surface of the magnet. Theuse of such a magnet in a rotary seal of the type described produces noflux reversals in the magnetically attractive member so that eddycurrents are not produced.

In accordance with a preferred arrangement, a pair of inner and outerradially spaced sleeve members of a material having a high magneticpermeability are provided for increasing the strength of the magneticfield. The inner sleeve member is positioned in engagement with theinner cylindrical surface of the magnet and the outer sleeve member ispositioned in engagement with the outer cylindrical surface of themagnet. The inner and outer sleeve members have end portions positionedadjacent one end surface of the cylindrical magnet. The sleeve membersserve to collect the magnetic field lines from along the axial length ofthe inner and outer cylindrical surfaces and concentrate the field atone end surface thereof. ln one arrangement, the inner and outer sleevemembers have end portions which project radially toward one another inoverlying relationship to one end surface of the cylindrical magnet.With such an arrangement, a sealing means may be trapped between an endsurface of the cylindrical magnet and the radially extending endportions of the sleeve members.

In one arrangement, the cylindrical magnet has a circular groove formedin one end surface thereof intermediate the inner and outercircumferential surfaces. The groove receives one portion of a circularsealing ring which has another portion projecting axially outward beyondthe end surface of the magnet member. In the preferred arrangement, thesealing ring is secured in the groove, as by adhesive or the like, toprevent relative rotation between the magnet member and the sealingring. Relative rotation between the magnet member and the sealing ringcould cause rapid deterioration of the magnet member during use thereofin a shaft seal of the type described.

It is a principle object of the present invention to provide a magneticseal for rotary shafts which is not subject to overheating or loss ofmagnetic attraction due to eddy currents.

It is also an object of the present invention to provide an improvedmagnet for use in seals of the type described.

It is also an object of the present invention to provide a magnetic sealfor rotary shafts which is more economical than previous constructions.

It is another object of the present invention to provide an improvedmethod for making a cylindrical magnet and providing it with a verystrong radial magnetization.

BRIEF DESCRIPTION OF THE DRAWING The invention may take physical form incertain parts and arrangements of parts, a preferred embodiment of whichwill be described in detail in this specification and illustrated in theaccompanying drawings which form a part hereof.

FIG. 1 is a cross-sectional elevational view showing a seal for a rotaryshaft having the improvement of the present invention incorporatedtherein;

FIG. 2 is a cross-sectional elevational view of the improved magnet ofthe present invention;

FIG. 3 is an end elevational view looking in the direction of arrows 3-3of FIG. 2;

FIG. 4 is a cross-sectional elevational view of a sealing ring for usewith the magnet of FIG. 2;

FIG. 5 is an end elevational view looking in the direction of arrows 55of FIG. 4;

FIG. 6 is a cross-sectional elevational view similar to FIG. 1 showinganother arrangement of a rotary shaft seal having the present inventionincorporated therein;

FIG. 7 is a cross-sectional elevational view showing the magnet of thepresent invention with means for increasing the field strength; and

FIG. 8 is a cross-sectional elevational view showing a mold in which themagnet of the present invention is formed.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawing,wherein the showings are for purposes of illustrating a preferredembodiment of the invention only and not for purposes of limiting same,FIG. 1 shows housing A of a fluid pump or the like. Housing A includes acavity 12 having suitable inlet and outlet ports in a known manner.Housing A is formed with a cylindrical bore 14 through which rotaryshaft 16 extends. Housing A further includes a circumferential recess 18supporting a bearing 20 in which shaft 16 is rotatably mounted. Shaft 16is rotatably driven by any suitable motor in a known manner and includesan impeller 22 mounted on one end thereof within cavity 12. Instructures of the type described, it is often desirable to preventleakage either into or out of cavity 12 along shaft 16. Therefore, aseal is provided along shaft 16 for preventing leakage which may becaused either by a high pressure or vacuum differential. It will berecognized that the fluid pump is only diagramatically described forpurposes of illustrating the present invention and the seal of thepresent invention is useable in a variety of environments where it isdesired to seal a rotary shaft. The present invention is also useful forpreventing leakage from bearings or the like.

In one arrangement, housing A is formed with a cylindrical recess 24 ofa larger diameter than bore 14. A cylindrical magnet member B isreceived on shaft 16 and positioned in recess 24. Magnet B includes aninner circumferential surface 26 and an outer circumferential surface28. Outer circumferential surface 28 is spaced radially outward frominner circumferential su rface 26 a distance which is substantially lessthan the axial length of magnet member B. Magnet member B furtherincludes opposed end surfaces 30 and 32. Outer circumferential surface28 is formed with a circumferential groove or recess 34 which receivesan O-ring 36 of neoprene or other suitable elastomeric material. O-ring36 is tightly compressed between the bottom of groove 34 and theperiphery of recess 24. Preferably, O-ring 36 is compressed sufficientlyto provide a frictional force which holds magnet B against rotation withshaft 16. It will also be recognized that it is possible to key magnet Bto housing A for preventing rotation thereof if so desired. In addition,it will be recognized that housing A may represent only one half of anaxially split housing so that two identical such housings may be boltedtogether with suitable gasketing between their contacting surfaces. Insuch an arrangement, the parts described may be positioned on shaft 16and placed in one half of the housing before bolting of the otherhousing half thereto. Inner circumferential surface 26 preferably has adiameter slightly larger than the diameter of shaft 16 so there will heno contact between shaft 16 and magnet member 8.

In accordance with one arrangement, magnet member B is formed with acircular groove or recess 38 in end surface 32 intermediate inner andouter circumferential surfaces 26 and 28. Circular groove 38 receivesone end portion of a cylindrical sealing ring 40. Sealing ring 40 ispreferably formed from such materials as polytetrafluoroethylene, or apolyamide having a lubricant such as graphite mixed therein, or agraphite. Sealing ring 40 is preferably secured in circu' lar groove 38against rotation relative to magnet member B. In a preferredarrangement, sealing ring 40 is adhesively secured within circulargroove 38 by applying adhesive within groove 38 and to one end portionof sealing ring 40. However, it will be recognized that mechanical meansmay be provided to prevent rotation of sealing ring 40 relative tomagnet member B as by extending a pin radially of magnet member 8through inner circumferential surface 26 and through groove 38 whensealing ring 40 is positioned therein. Likewise, it is possible toprovide a radially extending key projection on sealing ring 40 and anaxially extending recess in the outer wall of groove 38 for receivingthe key projection. With sealing ring 40 positioned in groove 38,sealing ring 40 includes a portion projecting axially beyond end surface32 as shown in FIG. 1.

A magnetically attractive member C, of substantially cylindrical shapeand of such material as case hardened steel, is also received on shaft16 adjacent magnet member B. Magnetically attractive member C includesan inner circumferential groove 43 which receives an O-ring 44 ofneoprene or other suitable elastomeric material. O-ring 44 is a tightfit on shaft 16 and is tightly compressed between the bottom of groove43 and the outer periphery of shaft 16. The frictional gripping providedby O-ring 44 on shaft 16 is preferably sufficient so that magneticallyattractive member C rotates with shaft 16. It will be recognized that itis also possible to key magnetically attractive member C to shaft 16 forrotation therewith if so desired. Magnetically attractive member C mayhave one end surface portion 42 polished so as to be very smooth if sodesired. With one end portion 46 of sealing ring 40 positioned incircular groove 38, and other end 48 of sealing ring 40 projectingoutwardly beyond end surface 32 of magnet member B, end surface 42 ofmagnetically attractive member C cooperates with end 48 of sealing ring40 to provide a radial seal.

With the arrangement described, the gripping of O- ring 36 against theperiphery of recess 24 may be such as to allow axial movement of magnetmember B along shaft 16. ln addition, gripping of O-ring 44 on shaft 16may be such as to permit axial movement of magnetically attractivemember C along shaft 16. It will be recognized that either magnet memberB or magnetically attractive member C, or both, may be capable ofrelative axial movement along shaft 16. Magnetic attraction betweenmagnet member B and magnetically attractive member C will draw these twomembers together until end 48 of sealing ring 40 contacts end surface 42of magnetically attractive member C. With the arrangement described,O-ring 44 prevents leakage along shaft 16, while O-ring 36 preventsleakage axially along recess 24. Engagement between sealing ring 40 andend surface 42 prevents radial leakage. In order to prevent a magneticshort circuit, housing A is made of diamagnetic material, or an insertof diamagnetic material is positioned in housing A around magnet member8. Such diamagnetic material may be nonmagnetic steel alloy, bronze orsynthetic plastic.

In operation, magnetically attractive member C and O-ring 44 rotate withshaft 16 while magnet B and O- ring 36 are nonrotating. Cooperationbetween end surface 42 of magnetically attractive member C and end 48 ofsealing ring 40 provide a sliding radial seal. The low friction materialof which sealing ring 40 is made, and polished end surface 42 ofmagnetically attractive member C, provide insufficient rotary frictionalclutching action to rotate magnet member B against the frictionalgripping action of O-ring 36. ln addition, the material of which magnetmember B is formed will wear away more rapidly than magneticallyattractive member C and securement of sealing ring 40 within circulargroove 38 prevents rapid deterioration of magnet member B.

In the arrangement described, magnet member B has an outer diameter ofapproximately 60 millimeters and an inner diameter of approximately 40millimeters. The axial length between end surfaces 30 and 32 isapproximately millimeters. Groove 38 has a depth of approximately 3millimeters, and sealing ring 40 has an axial length between endsurfaces 46 and 48 of approximately 4 millimeters. When sealing ring 40is positioned in groove 38, it projects outward from end sur' face 32not greater than I millimeter. This projecting distance of sealing ring40 is preferably even less than I millimeter so that end surfaces 32 and42 will be as close as possible for optimum magnetic attraction.

In accordance with the invention, magnet member 8 is formed of amaterial which is normally non-magnetic but which may be made magneticby subjecting it to a magnetic field. More specifically, magnet member Bis formed of powdered material such as manganese bismuth, bariumferrite, lead ferrite or strontium ferrite. This powdered material ismixed with a thermoplastic material such as polystyrene, superpolyamideor the like. Magnetic member B has the magnetic particles thereinradially oriented in the direction of their easy magnetization and isalso radially magnetized. That is, cylindrical magnet member B issubjected to a magnetic field extending radially from longitudinal axis51 radially outward toward outer circumferential surface 28.

In the arrangement shown in FIGS. 2 and 3, magnet member 8 is radiallymagnetized so that outer circumferential surface 28 defines a northmagnetic pole and inner circumferential surface 26 defines a southmagnetic pole. It will be recognized that these poles may be reversed ifso desired so that inner circumferential surface 26 would define a northmagnetic pole and outer circumferential surface 28 would define a southmagnetic pole. With magnet member B radially magnetized, magnetic fluxacts in substantially radial directions as indicated by arrows 52 inFIG. 2. That is, the magnetic field acts in a substantially radialdirection and extends from outer circumferential surface 28 to innercircumferential surface 26 outwardly of end surface 32. With thisarrangement, it will be recognized that pole changing does not occurduring relative rotation of magnetically attractive member C and magnetmember B. That is, end surface 42 of magnetically attractive member C isalways under the influence of a north magnetic pole in its outerperipheral area and under the influence of a southern magnetic pole atits inner peripheral surface. Therefore, magnetically attractive memberC does not move through any alternating magnetic field and eddy currentsare not developed in magnetically attractive member C. With no eddycurrents developed, the magnetic attraction between magnet member B andmagnetically attractive member C remains substantially constantregardless of the relative rotational speed between them. In addition,the absence of eddy currents in magnetically attractive member Cprevents heat from being generated in magnetically attractive member C.

In the arrangement shown in FIG. 1, it will be recognized that more thanone bearing may be provided if so desired, and that bearing 20 may bepositioned on the opposite side of magnetic member B and magneticallyattractive member C. Various arrangements are possible as is well knownto those skilled in the art.

In accordance with another arrangement, as shown in FIG. 6, a housing Dincludes a cylindrical bore 56 through which rotatable shaft 16 extends.Housing D includes a recess 58 for retaining bearing 60 in which shaft16 is rotatably journaled. Enlarged recess 62 in housing D around shaft16 has a ring 64 of case hardened steel secured against an end face 66thereof as by bolts 68. A magnet member E, of material identical to thatof magnet B and also being radially magnetized, is positioned on shaft16. A circumferential groove 70 in the inner peripheral surface ofmagnet member E receives an O-ring 72 of neoprene or similar elastomericmaterial. ()-ring 72 is compressed between the bottom of groove 70 andthe outer periphery of shaft 16 so that magnet member E will normallyrotate with shaft 16. A circular groove 74 in one end surface of magnetmember E receives a sealing ring 40 which is identical in constructionto the sealing ring of FIG. 4. Sealing ring 40 bears against thepolished outer surface 76 of steel ring 64. Magnetic attraction betweenmagnetic member E. and steel ring 64 causes magnet member E to shiftaxially along shaft 16 and bring sealing ring 40 into engagement withthe outer surface of steel ring 64. O-ring 72 prevents leakage axiallyalong shaft 16, and contact between sealing ring 40 and steel ring 64provides a radial seal. As in the previously described arrangement,sealing ring 40 is preferably secured against rotation within circulargroove 74 of magnet member E.

In the arrangements of both FIGS. I and 6, it will be recognized thatmagnet members 8 or E define a first element and that magneticallyattractive members C or 64 define a second element. In either case, oneof the elements is rotatable with the shaft and the other of theelements is fixed against rotation relative to the shaft. In addition,each situation includes a sealing means interposed between the rotatableelement and the shaft, and a second sealing means interposed between thefirst and second elements. In addition, at least one of the elements iscapable of shifting axially relative to the shaft under the influence ofmagnetically attractive force between the first and second elements.

In accordance with another arrangement, magnet member B of FIG. 2 isformed without groove 38 as shown in FIG. 7. In this arrangement acircular sealing ring J having a T-shaped cross-section is used in placeof sealing ring 40 of FIG. 4. T-shaped sealing ring .I includes a mainleg portion 86 extending axially outward from magnet end surface 32, anda pair of flange portions 90 and 92. Sealing ring .I may also be moldedinto a circular ring from such materials as polytetrafloroethylene or apolyamide impregnated with lubricant such as graphite. Sealing ring Jmay then be adhesively secured to end surface 32 of magnet B. It will berecognized that mechanical securing means may also be provided as byinserting screws through flanges 90 and 92 into the end portion ofmagnet B. In accordance with a preferred arrangement of the presentinvention, magnet member B is provided with a means for concentratinglines 52 of magnetic force as shown in FIG. 7. A cylindrical steel outersleeve 102 is positioned over magnet member B in engagement with asubstantial portion of outer circumferential surface 28. In thearrangement shown, the outer diameter of magnet member B fromcircumferential groove 34 to end surface 32 is approximately 58millimeters. Sleeve 102 has a wall thickness of approximately Imillimeter and an axial lengthof approximately ll millimeters. An innercylindrical sleeve 104 is positioned inside of magnet member B incontact with inner circumferential surface 26. Sleeve 104 has a wallthickness of approximately 1 millimeter and an axial length ofapproximately 20 millimeters. Sleeve members I02 and 104 are of highmagnetic permeability and serve to collect and concentrate lines 52 ofmagnetic force at end surface 32 of magnet member B. It will berecognized that it is possible to make sleeve members 102 and I04 atight fit on magnet member B if so desired and it is also possible toadhesively secure the sleeve members to inner and outer circumferentialsurfaces 26 and 28 if so desired. With the arrangement shown in FIG. 7,the diameter of inner circumferential surface 26 is such that innersleeve member 104 may be received therein and the internal diameter ofsleeve I04 will be greater than the outer diameter of shaft l6.

Inner and outer sleeve members 104 and I02 have end portions whichterminate adjacent end surface 32 of magnet member B. In a preferredarrangement, the end portions of sleeve members 102 and 104 projectradially inward toward one another as at 106 and 108. These radiallyextending portions 106 and 108 terminate short of one another to providea radial and circular opening through which main leg 86 of sealing ringI projects. Main leg 86 projects axially outward beyond the outersurfaces of radial portions 106 and 108 a distance not greater than Imillimeter for contacting an end surface of an adjacent magneticallyattractive member. In addition, radially extending portions 106 and 108trap flanges 90 and 92 of sealing ring I against end surface 32 ofmagnet member B. In the arrangement shown, outer sleeve 102 has an axiallength less than the axial length of inner sleeve 104. Outercircumferential surface 28 has a much greater area than innercircumferential surface 26 and the longer axial length of inner sleevemember 104 provides a pole concentration at end portion 108 which willbe substantially equal to that at end portion 106 of outer sleeve member102.

It will be recognized that sleeve members I02 and 104 may also be usedwith the embodiment of FIG. 2 in which sealing ring 40 is utilized. Insuch an arrangement, radially extending portions 106 and 108 of sleevemembers 102 and 104 will contact end surface 32 of magnet member B.Sealing ring 40 is then made longer axially to project not greater than2 millimeters from end surface 32 and not greater than I millimeter fromthe outer surfaces of radially extending portions 106 and 108. In thearrangement shown, sealing ring 40, and main leg 86 of sealing ring .I,each have a radial thickness of approximately 3 millimeters, and theterminal ends of radially extending portions 106 and 108 are spacedapart approximately 3 millimeters. It will be recognized that it is alsopossible to use sleeve members without radially extending portions 106and I08 although the magnetic attraction will be less than optimum.

In accordance with the invention, the cylindrical magnet member isradially oriented during molding thereof so that the magnetic fieldcapable of being produced by the magnet is greatly increased instrength. FIG. 8 shows a mold arrangement which includes a base plate112 of iron to which an iron cylindrical member 114 is secured as bybolts 116. Member 114 has a circumferential recess 118 receiving theouter peripheral portion of an iron circular plate 120 which is securedin position by bolts I22. Circular plate 120 has a central circular bore124 receiving a steel bushing 126. The mold includes a cylindrical core128 of hardened steel which is secured to base plate 112 as by bolt 130.The inner circumferential surface of bushing 126 is spaced radiallyoutward from the outer circumferential surface of core 120 to define amold cavity 132. The bottom of mold cavity 132 is formed by acylindrical ejecting ring 134 and the top by a projectingcircumferential ring portion 136 on upper mold plate 138. Both uppermold plate 138 and ejecting ring 134 are made of diamagnetic material,such as non-magnetic steel alloy or bronze. The lower portion of core128 is of a larger diameter than the upper portion thereof to provide acircumferential shoulder 140 against which the lower inner periphery ofejecting ring 134 abuts. This insures a constant height h for moldcavity 132 after each ejection of a magnet and each back movement ofejecting ring 134. Upper mold plate 138 is provided with a sprue 142 andan air relief opening 144. A conventional injection molding nozzlecooperates with sprue 142 to inject magnet forming material into cavity132.

An electrical coil 144 is positioned inside of ring 1 14. Coil 144includes a body portion 146 secured to base plate 112 as by bolts 148,and an energizing winding 150 carried by body portion 146. Coil bodyportion 146 may be of such material as aluminum alloy. Electrical leads152 and 154 for winding 150 extend through isolated bores as at 156 inring 114.

The ejecting arrangement includes four circumferentially spaced pins 158provided with threads on their upper end portions 160. Threaded endportions 160 are threaded into suitable threaded bores in ejecting ring134. Pins 158 extend through holes in disc 162 and have enlarged heads164 received in enlarged circular recesses 166 in disc 162. A seconddisc 168 is secured to disc 162 by bolts 170 so that enlarged heads 164are trapped between discs 162 and 168.

When coil 144 is energized, magnetic poles indicated in FIG. 8 byletters N & S are formed in plate 120 and core 128. This produces aradial magnetic aligning field in mold cavity 132. As previouslymentioned, the magnet material is preferably a powder of such materialsas manganese bismuth, barium ferrite, lead ferrite or strontium ferrite,and this material is mixed with a small portion of thermoplasticmaterial such as polystyrene or superpolyamide. The mixture is injectedinto cavity 132 through sprue 142. With the plastic still in a fluidstate, and an electrical current energizing coil 144 through leads 152and 154, the magnetic particles contained therein are capable ofmovement so that their preferred axes of magnetization are aligned bythe magnetic field extending radially across cavity 132 rather thanbeing randomly oriented. Maximum field strength is produced when themagnet is later radially magnetized. With the magnetic particlesradially oriented under the influence of the magnetic field in the mold,they will remain radially oriented as the plastic cools to a rigidstate. Once the plastic material has hardened or solidified, acylindrical ring of solidified plastic and powdered permanent magnetmaterial is provided, and the magnetic particles are radially oriented.

Once the magnet material in cavity 132 has solidified to a state inwhich the magnetic particles are held with their preferred axes ofmagnetization in alignment, the polarity of the electrical currentapplied to electrical leads 152 and 154 is reversed for a short time toreverse the direction of the magnetic field produced in cavity 132 bycoil 144. This reversal of polarity substantially removes anymagnetization which has been produced in the magnet material by thealigning field and removal of the solidified magnet material from cavity132 is easier. Upper mold plate 138 is then separated from plate 120 andthe ejecting device is operated to eject the solidified magnet materialfrom mold cavity 132. Ejecting ring 134, pins 158, and discs 162 and 168are moved in the direction of arrows 174 to eject a formed magnet fromcavity 132. These members, which define the ejecting device, are movedin the direction of arrows 176 after ejection of a magnet until ring 134abuts shoulder 140. The mold is then ready to form another magnet onceupper mold plate 138 is moved back to the closed position shown in FIG.8. The ejecting device may be operated mechanically or pneumatically. ina pneumatic arrangement, disc 168 is connected with the piston of adouble acting air cylinder which is capable of moving the ejectingdevice in the direction of either arrows 174 or 176.

Once the solidified cylindrical ring of magnet material is removed fromthe mold, it is radially magnetized. That is, it is subjected to amagnetizing field acting radially relative to the longitudinal axis ofthe cylindrical magnet member, and in the same direction as the aligningfield produced in cavity 132 by coil 144, so that the magnet member isprovided with an outer circumferential surface defining one magneticpole, and an inner circumferential surface defining another magneticpole.

While certain preferred arrangements have been described in detail onthis specification and illustrated in the accompanying drawing, it isobvious that modifications and alterations will occur to others skilledin the art upon the reading and understanding of this specification. Thepresent invention includes all such equivalent modifications andalterations and is limited only by the scope of the claims.

Having thus described my invention, 1 claim:

1. A cylindrical magnet formed of powdered magnetic material, saidmagnet having radially spaced inner and outer cylindrical surfaces andopposite end surfaces, said magnet being radially magnetized so that oneof said inner and outer cylindrical surfaces defines a north magneticpole and the other of said inner and outer cylindrical surfaces definesa south magnetic pole, a circular groove formed in one of said endsurfaces intermediate said inner and outer cylindrical surfaces, acircular sealing ring having a portion received in said groove and aportion projecting axially outward from said one end surface, and meansfixing said sealing ring in said groove against rotation relative tosaid magnet.

2. The device of claim 1 wherein said magnet is molded of anisotropicferrite permanent magnet particles dispersed in a plastic binder, saidparticles having preferred axes of magnetization oriented radiallybetween said inner and outer cylindrical surfaces of said magnet.

3. The device of claim 1 wherein said magnet defines a first element andsaid inner cylindrical surface defines the surface of a bore throughsaid magnet, a rotatable shaft extending through said bore, a secondelement defined by a circumferential magnetically attractive membersurrounding said shaft, said second element having an end surface facingand engageable with said sealing ring, one of said elements beingrotatable with said shaft and the other of said elements being fixedagainst rotation relative to said shaft, sealing means interposedbetween said one element and said shaft, and at least one of saidelements being shiftable axially of said shaft toward the other of saidelements under influence of magnetically attractive force between saidfirst and second elements.

4. The device of claim 3 and further including a pair of radially spacedsleeve members of high magnetic permeability engaging said inner andouter cylindrical surfaces of said magnet, said sleeve members havingsleeve end portions positioned adjacent said one end surface of saidmagnet.

5. The device of claim 4 wherein said sleeve end portions extendsubstantially radially toward one another and overlie said one endsurface of said magnet.

6. A cylindrical magnet formed of powdered magnetic material, saidmagnet having radially spaced inner and outer cylindrical surfaces andopposite end surfaces, said magnet being radially magnetized so that oneof said inner and outer cylindrical surfaces defines a north magneticpole and the other of said inner and outer cylindrical surfaces definesa south magnetic pole, a pair of inner and outer radially spaced sleevemembers of high magnetic permeability engaging said inner and outercylindrical surfaces of said magnet, said sleeve members having sleeveend portions positioned adjacent at least one of said end surfaces ofsaid magnet.

7. The device of claim 6 wherein said sleeve end portions projectsubstantially radially of said magnet toward one another in overlyingrelationship to said one end surface.

8. The device of claim 7 and further including circular sealing meanshaving a substantially T-shaped crosssectional shape and being attachedto said one end surface, said circular sealing means including a centralleg portion projecting axially outward from said one end surface and apair of side flange portions trapped between said one end surface andsaid sleeve end portions.

9. The device of claim 6 wherein said magnet is molded of anisotropicferrite permanent magnet particles dispersed in a plastic binder, saidparticles having preferred axes of magnetization oriented radiallybetween said inner and outer cylindrical surfaces of said magnet.

10. The device of claim 6 wherein said magnet defines a first elementand said inner cylindrical surface defines the surface of a bore throughsaid magnet, a rotatable shaft extending through said bore, a secondelement defined by a circumferential magnetically attractive membersurrounding said shaft adjacent said magnet, said second element havinga facing end surface facing said one end surface of said magnet, one ofsaid elements being rotatable with said shaft and the other of saidelements being fixed against rotation relative to said shaft, firstsealing means interposed between said one element and said shaft, secondsealing means interposed between said one end surface of said magnet andsaid facing end surface of said magnetically attractive member, and atleast one of said elements being shiftable axially of said shaft towardthe other of said elements under influence of magnetically attractiveforce between said first and second elements.

11. The device of claim 10 wherein said second sealing means is fixedagainst rotation relative to said magnet.

12. The device of claim 10 wherein said sleeve end portions extendsubstantially radially of said magnet toward one another, said secondsealing means comprising a circular member having a substantially T-shaped cross-sectional shape including a control leg portion projectingaxially of said shaft and a pair of side flange portions trapped betweensaid one end surface of said mafine and said sleeve end portipns.

. A c m rical magnet member mo ded of material including anisotropicferrite permanent magnet particles dispersed in a plastic binder, saidmagnet having radially spaced inner and outer cylindrical surfaces andopposite end surfaces, said particles having preferred axes ofmagnetization, substantially all of said particles having said preferredaxes of magnetization thereof aligned radially of said magnet memberbetween said inner and outer surfaces within said plastic binder, saidmagnet member being radially magnetized so that one of said inner andouter surfaces defines a north magnetic pole and the other of said innerand outer surfaces defines a south magnetic pole, a circular grooveformed in one of said end surfaces intermediate said inner and outersurfaces, a circular sealing ring having a portion received in saidgroove and a portion projecting axially outward from said one endsurface, and means fixing said sealing ring in said groove againstrotation relative to said magnet.

14. A cylindrical magnet member molded of material including anisotropicferrite permanent magnet particles dispersed in a plastic binder, saidmagnet having radially spaced inner and outer cylindrical surfaces andopposite end surfaces, said particles having preferred axes ofmagnetization, substantially all of said particles having said preferredaxes of magnetization thereof aligned radially of said magnet memberbetween said inner and outer surfaces within said plastic binder, saidmagnet member being radially magnetized so that one of said inner andouter surfaces defines a north magnetic pole and the other of said innerand outer surfaces defines a south magnetic pole, a pair of inner andouter radially spaced sleeve members of a material having high magneticpermeability, said inner sleeve member being in engagement with saidinner cylindrical surface and said outer sleeve member being inengagement with said outer cylindrical surface, and said sleeve membershaving end portions positioned adjacent at least one of said endsurfaces.

15. The magnet member of claim 14 wherein said end portions of saidsleeve members project radially toward one another in overlyingrelationship to said one end surface.

16. The magnet member of claim 15 and including sealing means ofsubstantially T-shaped cross-section attached to said one end surface,said sealing means including a central leg portion projecting axiallyoutward from said one end surface and a pair of side flange portionstrapped between said one end surface and said radially extending endportions of said sleeve members.

2. The device of claim 1 wherein said magnet is molded of anisotropicferrite permanent magnet particles dispersed in a plastic binder, saidparticles having preferred axes of magnetization oriented radiallybetween said inner and outer cylindrical surfaces of said magnet.
 3. Thedevice of claim 1 wherein said magnet defines a first element and saidinner cylindrical surface defines the surface of a bore through saidmagnet, a rotatable shaft extending through said bore, a second elementdefined by a circumferential magnetically attractive member surroundingsaid shaft, said second element having an end surface facing andengageable with said sealing ring, one of said elements being rotatablewith said shaft and the other of said elements being fixed againstrotation relative to said shaft, sealing means interposed between saidone element and said shaft, and at least one of said elements beingshiftable axially of said shaft toward the other of said elements underinfluence of magnetically attractive force between said first and secondelements.
 4. The device of claim 3 and further including a pair ofradially spaced sleeve members of high magnetic permeability engagingsaid inner and outer cylindrical surfaces of said magnet, said sleevemembers having sleeve end portions positioned adjacent said one endsurface of said magnet.
 5. The device of claim 4 wherein said sleeve endportions extend substantially radially toward one another and overliesaid one end surface of said magnet.
 6. A cylindrical magnet formed ofpowdered magnetic material, said magnet having radially spaced inner andouter cylindrical surfaces and opposite end surfaces, said magnet beingradially magnetized so that one of said inner and outer cylindricalsurfaces defines a north magnetic pole and the other of said inner andouter cylindrical surfaces defines A south magnetic pole, a pair ofinner and outer radially spaced sleeve members of high magneticpermeability engaging said inner and outer cylindrical surfaces of saidmagnet, said sleeve members having sleeve end portions positionedadjacent at least one of said end surfaces of said magnet.
 7. The deviceof claim 6 wherein said sleeve end portions project substantiallyradially of said magnet toward one another in overlying relationship tosaid one end surface.
 8. The device of claim 7 and further includingcircular sealing means having a substantially T-shaped cross-sectionalshape and being attached to said one end surface, said circular sealingmeans including a central leg portion projecting axially outward fromsaid one end surface and a pair of side flange portions trapped betweensaid one end surface and said sleeve end portions.
 9. The device ofclaim 6 wherein said magnet is molded of anisotropic ferrite permanentmagnet particles dispersed in a plastic binder, said particles havingpreferred axes of magnetization oriented radially between said inner andouter cylindrical surfaces of said magnet.
 10. The device of claim 6wherein said magnet defines a first element and said inner cylindricalsurface defines the surface of a bore through said magnet, a rotatableshaft extending through said bore, a second element defined by acircumferential magnetically attractive member surrounding said shaftadjacent said magnet, said second element having a facing end surfacefacing said one end surface of said magnet, one of said elements beingrotatable with said shaft and the other of said elements being fixedagainst rotation relative to said shaft, first sealing means interposedbetween said one element and said shaft, second sealing means interposedbetween said one end surface of said magnet and said facing end surfaceof said magnetically attractive member, and at least one of saidelements being shiftable axially of said shaft toward the other of saidelements under influence of magnetically attractive force between saidfirst and second elements.
 11. The device of claim 10 wherein saidsecond sealing means is fixed against rotation relative to said magnet.12. The device of claim 10 wherein said sleeve end portions extendsubstantially radially of said magnet toward one another, said secondsealing means comprising a circular member having a substantiallyT-shaped cross-sectional shape including a control leg portionprojecting axially of said shaft and a pair of side flange portionstrapped between said one end surface of said magnet and said sleeve endportions.
 13. A cylindrical magnet member molded of material includinganisotropic ferrite permanent magnet particles dispersed in a plasticbinder, said magnet having radially spaced inner and outer cylindricalsurfaces and opposite end surfaces, said particles having preferred axesof magnetization, substantially all of said particles having saidpreferred axes of magnetization thereof aligned radially of said magnetmember between said inner and outer surfaces within said plastic binder,said magnet member being radially magnetized so that one of said innerand outer surfaces defines a north magnetic pole and the other of saidinner and outer surfaces defines a south magnetic pole, a circulargroove formed in one of said end surfaces intermediate said inner andouter surfaces, a circular sealing ring having a portion received insaid groove and a portion projecting axially outward from said one endsurface, and means fixing said sealing ring in said groove againstrotation relative to said magnet.
 14. A cylindrical magnet member moldedof material including anisotropic ferrite permanent magnet particlesdispersed in a plastic binder, said magnet having radially spaced innerand outer cylindrical surfaces and opposite end surfaces, said particleshaving preferred axes of magnetization, substantially all of saidparticles having said preferred axes of magnetization thereof alignedradially of saiD magnet member between said inner and outer surfaceswithin said plastic binder, said magnet member being radially magnetizedso that one of said inner and outer surfaces defines a north magneticpole and the other of said inner and outer surfaces defines a southmagnetic pole, a pair of inner and outer radially spaced sleeve membersof a material having high magnetic permeability, said inner sleevemember being in engagement with said inner cylindrical surface and saidouter sleeve member being in engagement with said outer cylindricalsurface, and said sleeve members having end portions positioned adjacentat least one of said end surfaces.
 15. The magnet member of claim 14wherein said end portions of said sleeve members project radially towardone another in overlying relationship to said one end surface.
 16. Themagnet member of claim 15 and including sealing means of substantiallyT-shaped cross-section attached to said one end surface, said sealingmeans including a central leg portion projecting axially outward fromsaid one end surface and a pair of side flange portions trapped betweensaid one end surface and said radially extending end portions of saidsleeve members.